This invention relates to the treatment of subterranean formations. More particularly, this invention relates the use of acid foam for fracturing of subterranean formations.
Various methods have been utilized by the oil industry for increasing the oil and gas flow from subterranean formations. One approach is to hydraulically fracture such formations with various liquids with or without propping agents suspended therein. The hydraulic pressure causes fracturing of the rock; the initially formed fractures are then extended by the injection of liquids under pressure therein. Thus, fracturing throughout these specifications shall mean initiating the fracture, propagating it or enlarging it. A propping agent, if one is used, is deposited in the fractures to maintain the permeability of the formation after liquids are removed.
An improvement of this approach is to inject an acid solution into the formation under sufficient pressure to cause a fracture. The acid contained in the solution etches the fracture walls, thereby providing highly conductive channels. The degree of stimulation of the flow from the subterranean formation is strongly dependent upon the extend of acid penetration into the fracture; consequently, various methods have been devised to assure deep acid penetration. One such method involves the use of emulsions to shield the acid from the formation materials and thereby allow unreacted acid to penetrate deeply into the formation. Other methods to increase acid penetration involve the use of gelled acids and acids containing inhibitors which retard the reaction with the walls of the formation.
The enumerated attempts for increasing the productivity of oil and gas flow from subterranean formations suffer from several drawbacks. Thus, conventional hydraulic fracturing requires high viscosity liquids requiring extremely large pumping equipment to achieve satisfactory injection rates. It often necessitates a chemical treatment to improve the viscosity, gel strength and fluid loss properties before such liquids can be used for fracturing. The removal of the viscous fracturing fluid from the resulting fractures presents additional problems. Other difficulties are the tendency for the sand or propping agent, often incorporated in the fracturing fluid, to plug the entry to the fracture and the failure of a viscous fracturing fluid to uniformly deposit the propping agent within the fracture.
The problems associated with the use of emulsions, retarded and gelled acids are the size and high horsepower requirement of the pumping equipment and the difficulty in removal of the injected liquid. The present invention provides an improved acid fracturing process that alleviates many of the difficulties associated with prior art techniques.
Thus, one object of the present invention is to increase the productivity of a formation carrying oil, gas or other products.
Another object of the invention is to provide an improved formation fracturing operation.
A further object of the invention is to provide a method for fracturing subterranean formation, which results in the creation of deep and wide fractures.
Another object of the invention is to combine foam and chemical fracturing of formations to optimize results.
A still further object of the invention is to reduce the energy required for injection and the size of pumping equipment.
Still another object of the invention is to reduce the time and effort required for removal of the fracturing fluid.
A still further object of the invention is to provide a fluid which readily penetrates the created fractures and the existing cracks in the formation and uniformly deposits the propping agent contained therein.
Still another object of the invention is to provide a fracturing fluid which moderates the rate of reaction between the formation minerals and the acid contained in the fluid foam until full penetration of the fracture is obtained.
A still further object of the invention is to minimize the damage to subterranean formations by liquid fracturing media.
Still another object of the invention is to decrease the amount of acid needed for fracturing of a formation.
A still further object of the invention is to enable fracturing of formations with acid-foam even at elevated temperatures such as 300.degree. F. (149.degree. C.) to 500.degree. F. (260.degree. C.).
Other objects and advantages of this invention will be apparent to one skilled in the art upon studying this disclosure.